1. Technical Field
The present invention relates to the technical fields of electrooptic devices, such as organic electroluminescent (EL) devices, production methods therefor, and various electronic apparatuses including the electrooptic devices.
2. Related Art
In electrooptic devices, such as organic EL devices and silicon light-emitting devices, that include solid thin films and are driven and controlled by active elements such as TFTs, the electrodes and power supply wires of the electrooptic devices are composed of thin films. Even when these electrodes and power supply wires are composed of low-resistance metal materials, the resistance of the electrode and power supply wire causes the power voltage to decrease with the increase in size and output (brightness) of the electrooptic devices. This also affects the operation properties of the electrooptic devices. When the electrooptic devices is a display device of an active drive type in which power is supplied to a plurality of pixels arranged in a matrix over the entire image display region including the end portions, the voltage drop is particularly large at a location far from the power terminal. As a result, unevenness in brightness in the image display region readily occurs.
FIG. 6 shows the rate of decrease in brightness in the entire display during the full white display according to the structure of a related art, and FIG. 7 shows an example of unevenness in brightness. The difference in brightness between the display center and display end portions is preferably up to 3-2% in realizing a high quality display by increasing the size of a high-definition, light-emitting display device, such as a high definition television (HDTV). Even when the current of the light-emitting device of each pixel is 15 μA or lower, the power current in a display device having a diagonal size of 40 inches or more is on the ampere order. Thus, the resistance of the power supply wire for supplying power to each column of the pixels must be 11Ω or less and the power voltage drop must be 0.2 V or less. Moreover, as shown in FIG. 7, when a white square is displayed at the center of the red back ground over the entire image display region, bright red regions appear at the left and right of the white square and dark red regions appear above and below the white square because of the unevenness in brightness described above.
Consequently, in attempting to apply the device to a thin-film light-emitting device of an active drive type, such as an organic EL display device, by increasing the size, the thickness of the wiring (power supply wire) cannot be simply increased. The feasible thickness is about 200 to 300 nm from the standpoint of economically planarizing the step differences. Furthermore, in order to form a full color display, the width of the power supply wire for each pixel column must be one third of the width of the pixel or less. Accordingly, in an active light-emitting devices in the related art, the difference in brightness between high-brightness pattern and display patterns around the high-brightness pattern shown in FIG. 7 is at least 5% to 10% due to the limitations in thickness and width of the power supply wire and the resistance of the wiring materials. Thus, the display quality is significantly degraded, and increasing the size, the resolution, and/or the brightness of the device is difficult.
In view of the above, various techniques for decreasing the resistance of the power supply wire have been proposed (refer to Japanese Unexamined Patent Application Publication Nos. 11-329743, 5-307997, 2002-40961, and 2004-178839.